Utilisation of methane in mine air



NOV. 30, 1965 Q c, MIDDLETON 3,220,458

UTILISATION OF METHANE IN MINE AIR Filed April 2, 1964 HEAT EXTRACTOR INVENTOR:

CHARLES CRAIB MIDDLETON QMQ ATTORNEY.

United States Patent 3,220,458 UTILISATION 0F METHANE IN MINE AIR Charles Craib Middleton, 36 Stafford Road, Ellesmere Park, Eccies, England Filed Apr. 2, 1964, Ser. No. 357,862 Claims priority, application Great Britain, Apr. 6, 1963,

13,770/63; Sept, 5, 1963, 35,051/63 Claims. (Cl. 158-75) This invention concerns a method of and apparatus for economically utilising the methane in spent mine air, and simultaneously, if desired, drained methane or other convenient fuel, if the latter is available.

It is well known that, in coal mines, the air must constantly be refreshed in order to keep the percentage of methane gas in the air well below its combustion proportion at ordinary temperatures. In practice, it is usual to maintain the percentage of methane below 1%. This necessitates considerable ventilation of the mine and the ventilating fans of a large mine have to deal with up to tons of air per minute in order to maintain the methane below the 1% level of concentration.

In coal mines, the amount of methane which will be released per ton of coal mined in working a particular coal seam is fairly constant, and a portion of this methane can be drained off before its release, on normal working of the seam. However, in general, such drained methane is not readily saleable but as the amount of ventilation necessary in the mine, is thereby reduced, drainage is practised.

It is an object of the present invention to utilise, in an economical manner, such methane both in its drained form and in its proportion of up to 1% in normal spent mine air. By spent mine air is meant the air which is exhausted from the mine by the ventilation apparatus of the mine.

Although a methane/ air mixture will not burn at ordinary temperatures if the methane is less than about 3%, if the temperature is raised to more than about 1000 C., the mixture will completely combust and such combustion give out heat.

According to the present invention, spent mine air is raised to a temperature in excess of that at which the small proportion of methane contained therein will combust, and is allowed to combust, the heat energy produced by combustion being converted to electrical or mechanical energy.

In addition, drained methane gas or other convenient fuel can be burnt with the spent mine air so that its heat of combustion can also be utilised. If this is effected, the thermal efficiency of the process is greatly improved.

The method of the invention is most advantageously carried out in apparatus also in accordance with the invention, such apparatus comprising means to introduce spent mine air into and remove spent mine air from a combustion space, means for removing heat produced by combustion of spent mine air in the combustion space for use, and means for exchanging heat between spent mine air being introduced into the combustion space and spent mine air being removed from the combustion space.

In a preferred form the apparatus comprises a first heat exchanger whereinto the spent mine air is passed for raising the temperature thereof to the combustion temperature of the mixture so as to cause the same to combust, a second heat exchanger wherein some of the heat of combustion is extracted from the mixture, for conversion to electrical or mechanical energy, and a third heat exchanger wherein as much as is practical of the remaining heat content of the products of combustion is extracted.

However, for highly eflicient working of the apparatus,

the loading on the first and third heat exchangers is very high and consequently such exchangers are large.

Accordingly, a supplementary heat exchanger may be provided for transferring heat from the outgoing gas from the apparatus directly to the gas entering the apparatus.

Such a supplementary heat exchanger greatly reduces the load on, and consequently the size of, the first and third heat exchangers.

The first, third and supplementary heat exchangers may be integral.

Conveniently, means are provided whereby the flow of spent mine air can be reversed, the first and third heat exchangers then reversing their actions.

In a preferred embodiment, the first and third heat exchangers are in the form of regenerators which each comprise an insulated container containing a refractory substance of nature such as to offer little resistance to the flow of mine air therethrough but capable of effecting an efficient heat exchange with the mine air.

There are preferably provided, in or adjacent those ends of the first and third heat exchangers which are adjacent the second heat exchanger, burners for the combustion of gas or oil, so that the temperature of the said ends of both heat exchangers can, initially, be raised to the combustion temperature of the methane/air mixture. The said ends of the first and third heat exchangers define alternative combustion zones.

There may also be means for introducing drained methane into the spent mine air prior to the combustion zone of the apparatus. Alternatively, the drained methane can be introduced through the burners or at other suitable points.

The second heat exchanger preferably comprises a steam generator or other water heating boiler, or, alternatively, it may comprise an air pre-heater for feeding hot air to a further apparatus, e.g. a gas turbine.

It is arranged that the second heat exchanger, advantageously extracts 30% or more of the heat of combustion of the spent mine air.

The invention will be described further, by way of example, With reference to the accompanying drawings wherein:

FIG. 1 is a side elevation of a first embodiment of apparatus of the invention;

FIG. 2 is a plan view of the apparatus of FIG. 1;

FIG. 3 is a diagrammatic plan of a second embodiment of the apparatus;

FIG. 4 is a diagrammatic plan of a third embodiment of the apparatus; and

FIG. 5 is a detail plan of an alternative valve means for the apparatus of the invention.

As shown in FIGS. 1 and 2, apparatus for economically utilising methane from spent mine air, constructed in accordance with the present invention, comprises an inlet 11 whereinto spent mine air from a cool mine ventila tion system can be fed by means of a pump or fan 12.

The inlet 11 is selectively connectable by valve means 13 to either one of two identical heat exchangers 14 and 15 which, in the apparatus, because of their positions are referred to as a first and a third heat exchanger being numbered 14 and 15 respectively in the drawings. Each of these exchangers 14, 15 is in the form of a regenerator i.e., it comprises a container with an insulated exterior surface and contains a plurality of geometrically shaped chequers of refractory materials constucted so as define air passageways which offer low resistance to the passage of air therethrough but which present a considenable surface area over which heat exchange can take place between themselves and the air passing therethrough. Instead of refractory materials a metal filling can be employedat the cold ends 14a and 15a of the exchangers 14, 15. If desired, each exchanger 14, 15 can be surrounded by an external annulus wherethrough spent mine air may be passed to initially pre-heat the same. In this way, external heat losses are reduced, but under usual conditions the insulation of the regenerators by usual means has been found to be satisfactory.

The first and third heat exchangers 14, 15 are connected together at those ends 14b and 15b which are remote from the inlet (which ends 14b, 15b as will be seen later, are adjacent as far as air flow is concerned) by a passage 16 which is interrupted by a second heat exchanger 17. The heat extractor is ararnged to feed riser or water boiler is associated with the second heat exchanger 17. The heat exchanger is arranged to feed steam or hot water to auxiliary mine equipment (not shown) and thus to generate power for immediate use or for sale.

At either side of the second heat exchange-r 17, in the passage 16, are provided first and second ignition initiating means 14' and 15' respectively, which may be in the form of gas burners (not shown in FIGS. 1 and 2) for initially raising the temperature of both the first and third heat exchangers 14, 15.

The valve means 13 which connects the first or third heat exchanger 14 or 15 to the inlet 11 simultaneously connects the third or first heat exchanger 15 or 14 respectively to an outlet 18 wherefrom combusted spent mine air can be exhausted to the ambient atmosphere through a chimney (not shown). The valve means is of the type known as butterfly and is actuated by means of a vertical spindle 13a.

In order for the apparatus to work, spent mine air (containing, for example, /2% to 1% of methane) must be raised to a temperature whereat the mixture will combust. Normally, the spent mine air has a temperature of approximately 15 C. and this must be raised at least to 1000 C.

In order for the apparatus to work efiiciently combusted spent mine air exhausted therefrom should have a temperature as low as possible. In actual practice, it is arranged that the temperature of this air should be less than 100 C. Surface heat losses of the apparatus must also be kept to a minimum, and therefore the first, second and third heat exchangers 14, 17 and 15 are well insulated from the surrounding atmosphere in a conventional manner.

Initially, the apparatus is started up by passing a current of spent mine air therethrough and that gas burner on the outlet side of the second heat exchanger 17 is ignited. Supposing that the current of air flows through the first, second and third heat exchangers 14, 17 and 15 in that order and that the gas burner between the second and third heat exchangers 17, 15 is ignited, the temperature of the refractory material in the third heat exchanger 15 will be raised. Direction of air flow and selection of burner is reversed by means of the butterfly valve 13, for example, every half hour, until working temperatures are reached, i.e. the temperature at which the methane in the mine air is completely combusted without having recourse to the burners. The apparatus is then self-supporting and the burners can be extinguished. As the combusted spent mine air passes through the second heat exchanger 17, some of the heat content (at least 30%) thereof is removed and is utilised for raising steam or providing hot water.

Each regenerator 14 or 15 may be of conventional construction except in that the filling at the hot ends 14b or 15b must be of a good refractory material, whereat the filling at the cold ends 14a, 15a may be of a cheaper and less heat resistant material.

The filling may be of checquer bricks, which are readily available, but extruded ceramic pipes having irregular or circular sectioned apertures or bores may also be used, as such pipes may be arranged to have a low resistance to a flow of mine air being passed therethrough.

The pipes may be in sectional form, and slight misalignment of the sections is desirable in order to create turbulence in the flow. The diameter of the regenerators may be decreased form the cold ends 14a, 15a towards the hot ends 14b, 15b, in order to increase the velocity of the flow at the hot ends 14b, 15b.

Traps, for removal of accumulated dust and ashes, may be provided at one or each end of the heat exchangers 14, 15 or 17 and further traps may be disposed along the length thereof, particularly if a gap is left in the refractory filling. Such a gap may be of cylindrical form and defined, at a convenient point along the length of the first or third regenerators 14 or 15, be tween the hot end filling and the rest of the filling, and the gap will generate turbulence and provide a place whereat the mine air. may remix prior to the passing through the other parts of the filling in the regenerator.

The refractory filling may be of any desired form, but the fillings described are preferable as they provide a large refractory surface area and create turbulent conditions within the mine air flows in order that high heat transfer rates between the filling and the mine air may be achieved, whilst generating only a minimum resistance to mine air flow through the regenerator.

As shown in FIGS. 3 and 4, the apparatus may also include a counterflow supplementary heat exchanger 19. As the heat exchanger 19 works at the temperatures less than that of cold ends 14a, 15a of the regenerators 14, 15, it may be of mild steel construction, and thus of inexpensive construction. While other refractory fillings can be used the forms described hereinbefore are to be preferred since they provide a low resistance to gas flow therethrough.

If such a supplementary heat exchanger 19 is not used, the results demanded from the first and third heat exchangers 14, 15 for efficient operation are such that the size of these exchangers is necessarily great, as will be apparent from a study of the next paragraphs.

After passing through the second heat exchanger 17, the combusted spent mine air is cooled as much as possible, for example, to below C. on passing through the heat exchanger 14 or 15 connected with the outlet so that the exhausted air has a relatively low heat content. This maintains (or raises) the temperature of the refractory material or filling in the hottest zone or hot end 14b or 15b of the outlet connected exchanger 14 or 15 to a temperature such that, on reversal of the direction of air flow, the methane content of the incoming air will be completely combusted. Now the temperature drop across the third heat exchanger 15 (or the first heat exchanger 14) is of the order of 900 C. in the example given. Consequently, the area of the transferring surface of the exchanger must be great compared with the volume flow of gas through the exchanger, that is to say, the exchanger must be physically large.

However, if the supplementary heat exchanger 19 is used, the drop in temperature across the third heat exchanger 15 (or the first heat exchanger 14) is reduced by a third. Moreover, this reduction is effected over the temperature range of least heat transference, so that the size of the third (and first) heat exchanger 15 (and 14) can be greatly reduced, but the increase in size of the supplementary heat exchanger 19'need not be nearly so great since no heat storage capacity is required of this exchanger 19.

With reference to the embodiment shown diagrammatically in FIG. 3 the valve means 13 is connected by pipes 20, 20 to the supplementary heat exchanger 19 which is in turn connected by pipes 21, 22 to the regenerators 14, 15 respectively.

In the embodiment of FIG. 4, an alternative arrangement has been adopted in so far as the supplementary heat exchanger 19 (is connected by the pipes 20 to the valve means 13 which is in turn connected to the regenerators 14, 15 by the pipes 21, 22.

It will be appreciated that the hot ends 14b, 15b include combustion chambers or zones wherein combustion will take place, but such combustion will continue whilst the hot mine air is passing through the pipes 16 and possibly the second heat exchanger 17 also.

FIG. shows an alternative valve means 13b for reversing the direction of flow, and comprises a pair of poppet valves 23, 23 having respective pairs of seats 24 arranged about a partition 25. The valves 23 are mounted upon respective runs of an operating cable 26 located upon and driven by two pulleys Z7, 27 the valves 23 being biased to a mounting point on the cable 26 by means of springs 28, in order to achieve a satisfactory seal.

During the whole time the apparatus is in operation, considerable quantities of heat are extracted by the second heat exchanger making this process efficient.

The invention is, as aforesaid, not confined to the precise details of the foregoing example and variations can be made thereto. For instance, dust extractors or filters may be provided in the inlet to remove dust from the spent mine air as such dust may tend to clog the heat exchangers.

The gas burners may be replaced by oil burners.

Previously drained methane may be added to the spent mine air or it may be introduced into the hot zone of that exchanger connected to the inlet or, if storage facilities are available, may be used through the burners for starting up the apparatus.

Other valve means may be provided to reverse the flow of spent mine air.

The refractory material contained in the regenerators may take other forms than that described.

The second heat exchanger, instead of being steam raiser or water boiler, may comprise an air preheater for feeding hot air to a gas turbine engine or the like.

Other variations are possible within the scope of the present invention. For example, the supplementary counterfiow heat exchanger may be constructed so as to have a combustion zone and corresponding hot end of ceramic materials and may be connected directly to the second heat exchanger to the exclusion of the first and third heat exchanger or regenerators already described. Thus, the supplementary heat exchanger will serve as the first and third heat exchangers.

In this embodiment, only one combustion chamber, one gas or oil burner, and no valve means will be required. However, the construction of large size counterfiow heat exchangers of ceramic materials is difficult and expensive if gas leakages and their associated losses are to be avoided. For this reason the regenerators are preferred.

From this it will be appreciated that there is provided, in a mine, or otherwise, apparatus for utilizing spent mine air comprising; pump means to accumulate spent mine air, spent mine air input means, spent mine air output means, said spent mine air input means being connected to said pump means to receive spent mine air accumulated thereby, valve means, first conduit means, second conduit means, said valve means being operative to selectively connect said input means to one of said conduit means and said output means to the other of said conduit means, first heat exchange means located either in both said conduit means or said input and output means to transfer only heat between spent mine air in either said conduit means or said input and output means, first combustion chamber means located in said first conduit means, second combustion chamber means located in said second conduit means, first regenerative heat exchanger means located in said first conduit means, second regenerative heat exchanger means located in said second conduit means, first ignition initiation means associated with said first combustion chamber means, second ignition initiation means associated with said second combustion chamber means, both said regenerative heat exchanger means including a refractory filling in at least part thereof, said combustion chamber means being integral with said respective ones of said regenerative heat exchanger means, second heat exchanger means connected with said first and second conduit means to form a flow path for spent mine air therethrough and heat extraction means associated with said second heat exchanger means to receive heat transferred thereto from spent mine air combusted in at [least one of said combustion chamber means.

I claim:

1. Apparatus for utilizing a spent mine air mixture of less than 3.0 percent methane and remaining parts air comprising, pump means to accumulate the spent mine air mixture, spent mine air mixture input means, spent mine air mixture output means, said spent mine air mixture input means being connected to said pump means to receive the spent mine air mixture accumulated thereby, valve means, first conduit means, second conduit means, said valve means being operative to selectively connect said input means to one of said conduit means and said output means to the other of said conduit means, first regenerative heat exchanger means located in said first conduit means, second regenerative heat exchanger means located in said second conduit means, said first and second regenerative heat exchanger means raising the temperature of the mixture to the combustion temperature of the latter, first combustion chamber means located in said first conduit means, second combustion chamber means located in said second conduit means, first ignition initiation means associated with said first combustion chamber means, second ignition initiation means associated with said second combustion chamber means, both said regenerative heat exchanger means including a refractory filling comprising a plurality of geometrical-1y shaped checquers of refractory materials in at least part thereof, said combustion chamber means being integral with respective ones of said regenerative heat exchanger means, heat exchanger means connected with said first and second conduit means to form a low resistance flow path for the spent mine air mixture therethrough and heat extraction means associated with said heat exchanger means for extracting at least 30 percent of the heat of combustion transferred thereto from the spent mine air mixture combusted in at least one of said combustion chamber means.

2. Apparatus for effecting the combustion of a spent mine air mixture of less than 1.0 percent methane and remaining parts air comprising, pump means to accumulate the spent mine air mixture, spent mine air mixture input means, spent mine air mixture out-put means, said spent mine air mixture input means being connected to said pump means to receive the spent mine air mixture accumulated thereby, valve means, first, conduit means, second conduit means, said valve means being operative to selectively connect said input means to one of said conduit means and said output means to the other of said conduit means, first regenerative heat exchanger means located in said first conduit means, second regenerative heat exchanger means located in said second conduit means, said first and second regenerative heat exchanger means each including a refractory filling in at least a part thereof adapted to raise the temperature of the spent mine air mixture to a combustion temperature of at least 1000 C., first combustion chamber means located in said first conduit means, second combustion chamber means located in said second conduit means, first ignition initiation means associated with said first combustion chamber means, second ignition initiation means associated with said second combustion chamber means, said combustion chamber means being integral with respective ones of said regenerative heat exchanger means, heat exchanger means connected with said first and second conduit means to form a flow path for the spent mine air mixture therethrough and heat extraction means associated with said heat exchanger means for receiving heat transferred thereto from the spent mine air mixture combusted in at least one of said combustion chamber means, the products of combustion leaving said heat extraction means being within 80 C. of the spent mine air mixture accumulated by said pump means.

3. Apparatus for effecting the combustion of a spent mine air mixture of from 0.5 per-cent to 1.0 percent methane and air comprising, pump means to accumulate the spent mine air mixture, spent mine air mixture input means, spent mine air mixture output means, said spent mine air input means being connected to said pump means to receive spent mine air accumulated thereby, Valve means, first conduit means, second conduit means, said valve means being operative to selectively connect said input means to one of said conduit means and said output means to the other of said conduit means, first heat exchange means located in said input and output means to transfer heat between the spent mine air mixture in said input and output means, first regenerative heat exchanger means located in said first conduit means, second regenerative heat exchanger means located in said second conduit means, both said regenerative heat exchanger means including a refractory filling in at least part thereof, said refractory fillings comprising a plurality of geometrically shaped checquers of refractory materials constructed to define passageways which offer low resistance to the passage of the spent mine air mixture therethrough and adapted to raise the temperature of the spent mine air mixture above 1000 C., first combustion chamber means located in said first conduit means, second combustion chamber means located in said second conduit means, first ignition initiation means associated with said first combustion chamber means, second ignition initiation means associated with said second combustion chamber means, said combustion chamber means being integral with respective ones of said regenerative heat exchanger means, second heat exchanger means connected with said first and second conduit means to form a flow path for the spent mine air mixture therethrough and heat operable work storage means associated with said second heat exchanger means to be operated by heat transferred thereto from the spent mine air mixture combusted in at least one of said combustion chamber means.

4. Apparatus for utilizing a spent mine air mixture of from 0.5 percent to 1.0 percent methane and air by raising the temperature of the mixture from approximately C. to a combustion temperature of at least 1000 C. comprising, pump means to accumulate the spent mine air mixture, spent mine air mixture input means, spent mine air mixture output means, said spent mine air mixture input means being connected to said pump means to receive the spent mine air mixture accumulated thereby, valve means, first conduit means, second conduit means, said valve means being operative to selectively connect said input means to one of said conduit means and said output means to the other of said conduit means, first heat exchange means located in both said conduit means to transfer heat between the spent mine air mixture in said conduit means, first regenerative heat exchanger means located in said first conduit means, second regenerative heat exchanger means located in said second conduit means, both said regenerative heat exchanger means including a refractory filling in at least part thereof, said refractory fillings comprising a plurality of checquer bricks arranged to define irregular cross-sectioned bores which generate a minimum resistance to the mine air mixture flowing through said first and second regenerators while creating turbulent conditions in the mine air mixture flows to attain high heat transfer rates between said refractory fillings and the mine air mixture thereby to raise the temperature of the mine air mixture to at least 1000 C., first ignition initiation means associated with said first combustion chamber means, second ignition initiation means associated with said second combustion chamber means, said combustion chamber means being integral with respective ones of said regenerative heat exchanger means, second heat exchanger means connected with said first. and second conduit means to form a flow path for the spent mine air mixture therethrough and heat engine means associated with said second heat exchanger means to be operated by heat transferred thereto from the spent mine air mixture combusted in at least one of said combustion chamber means.

5. A method of utilizing a spent mine air mixture of less than 1.0 percent methane and remaining parts air comprising the steps of, passing a current of the mixture at an initial temperature of approximately 15 C. in one direction through a series of three heat exchange units containing a high transference refractory material in at least a portion thereof, igniting ignition initiating means disposed between the first and second and second and third heat exchangers to ignite the mixture, reversing the direction of flow of the mixture through the heat exchangers at regular intervals to raise the temperature of the refractory materials in the first and third heat exchangers until a temperature of at least 1000 C. is attained in the first and third heat exchangers, extin- 'guishing the ignition initiating means, extracting at least 30 percent of the heat of combustion of the mixture at the second heat exchange unit, and extracting a major proportion of the remaining heat content of the products of combustion of the mixture at the third heat exchange unit.

References Cited by the Examiner UNITED STATES PATENTS 1,542,953 6/1925 Puening 15s 7.5 1,561,389 11/1925 Wollers 15s -10s 2,895,544 7/1959 Parsons 1584.5

FOREIGN PATENTS 1,048,427 8/1953 France.

FREDERICK -L. MATTESON, 111., Primary Examiner. MEYER PERLIN, Examiner. 

1. APPARATUS FOR UTILIZING A SPENT MINE AIR MIXTURE OF LESS THAN 3.0 PERCENT METHANE AND REMAINING PARTS AIR COMPRISING, PUMP MEANS TO ACCUMULATE THE SPENT MINE AIR MIXTURE, SPENT MINE AIR MIXTURE INPUR MEANS, SPENT MINE AIR MIXTURE OUTPUT MEANS, SAID SPENT MINE AIR MIXTURE INPUT MEANS BEING CONNECTED TO SAID PUMP MEANS TO RECEIVE THE SPENT MINE AIR MIXTURE ACCUMULATED THEREBY, VALVE MEANS, FIRST CONDUIT MEANS, SECOND CONDUIT MEANS, SAID VALVE MEANS BEING OPERATIVE TO SELECTIVELY CONNECT SAID INPUT MEANS TO ONE OF SAID CONDUIT MEANS AND SAID OUTPUT MEANS TO THE OTHER OF SAID CONDUIT MEANS, FIRST REGENERATIVE HEAT EXCHANER MENAS LOCATED IN SAID FIRST CONDUIT MEANS, SECOND REGENERATIVE HEAT EXCHANGER MEANS LOCATED IN SAID SECOND CONCUIT MEANS, SAID FIRST AND SECOND REGENERATIVE HEAT EXCHANER MEANS RAISING THE TEMPERATURE OF THE MIXTURE TO THE COMBUSTION TEMPERATURE OF THE LATTER, FIRST COMBUSTION CHAMBER MEANS LOCATED IN SAID FIRST CONDUIT MEANS, SECOND COMBUSTION CHAMBER MEANS LOCATED IN SAID SECOND CONDUIT MEANS, FIRST IGNITION INITIATIN MEANS ASSOCIATED WITH SAID FIRST COMBUSTION CHAMBER MEANS, SECOND IGNITION INITIATION MEANS ASSICIATED WITH SAID SECOND COMBUSTION CHAMBER MEANS, BOTH SAID REGENERATIVE HEAT EXCHANGER MEANS INCLUDING A REFRACTORY FILLING COMPRISING A PLURALITY OF GEOMETRICALLY SHAPED CHECQUERS OF REFRACTORY MATERIALS INAT LEAST PART THEROF, SAID COMBUSTION CHAMBER MEANS BEING INTEGRAL WITH RESPECTIVE ONES OF SAID REGENERATIVE HEAT EXCHANGER MEANS, HEAT EXCHAGER MEANS CONNECTED WITH SAID FIRST AND SECOND CONDUIT MEANS TO FORM A LOW RESISTANCE FLOW PATH FOR THE SPENT MINE AIR MIXTURE THERETHROUGH AND HEAT EXTRACTION MENAS ASSOICATED WITH SAID HEAT EXCHANGER MEANS FOR EXTRACTING AT LEAST 30 PERCENT OF THE HEAT OF COMBUSTION TRANSFERRED THERETO FROM THE SPENT MINE AIR MIXTURE COMBUSTED IN AT LEAST ONE OF SAID COMBUSTION CHAMBER MEANS. 